In an attempt to gain an understanding of specific anatomic site of rotational remodelling, experimental rotational femoral osteotomies are performed on the femurs of immature dogs, one limb serving as a control, the second hind limb as a rotation side either receiving 45 degrees of internal or 45 degrees of external rotation. Radiographic markers are used to measure the precise area of rotation throughout the length of the femur and are placed intra-operatively at the time of osteotomy. Thin longitudinal sections of bone, both in longitudinal cross-sections, will be analyzed with routine histologic techniques following sacrifice of the animal. The animals will be allowed variable periods of development through which radiographic analysis of rotation will be accomplished. In addition to the routine histology sections, similar sections will be analyzed with in vivo tetracycline stain to attempt to elucidate the specific growth rate and remodelling rate of each region. It is hoped that this information will add to the understanding of the rotational alignment and modelling of growing bone.